1. Field of the Invention
The present invention relates to an organic electro luminescence device and a method of fabrication thereof.
2. Discussion of the Related Art
As large-size display devices are in demand, flat panel display (FPD) devices, which occupy less space than conventional displays, are increasingly required. Until now, liquid crystal display (LCD) devices are most highlighted due to their low-power consumption and light weight. However, since the LCD devices are a light receiving device, not a light emitting device, and have disadvantages in brightness, contrast, viewing angle, large-size area and the like, a new flat panel display device is being actively developed in order to overcome such disadvantages of the LCD devices.
One type of the flat panel display devices, organic electro luminescence (OEL) devices are being rapidly developed, and several finished products have been already delivered to the market. Since the organic electro luminescence devices are a self-luminescence type, they have excellent viewing angle, contrast and the like in comparison with the LCD devices. Because the organic electro luminescence devices do not need a backlight assembly, they are lightweight and slim, and have low power consumption. Additionally, since the organic electro luminescence devices can operate at a direct-current low voltage and at a high response speed, and are comprised of solid materials in all, they have high resistance to an external impact, a wide operational temperature range, and especially low manufacturing cost. Furthermore, a manufacturing method of the organic electro luminescence devices is very simple, since all it needs is deposition and encapsulation units, unlike the LCD devices or plasma display panels (PDP).
In the meantime, the organic electro luminescence devices are mainly driven in a passive matrix way without using a switching device such as a thin film transistor. The passive matrix OEL devices are configured in a matrix form where scan lines and signal lines intersect with each other. However, the passive matrix OEL devices have many limitations in resolution, power consumption, life expectancy and the like. Accordingly, active matrix OEL devices, which have switching devices, are being studied and developed as a next generation display requiring a high resolution or a large-size screen. In general, the active matrix OEL devices have a thin film transistor in every pixel to switch each of the pixels. The thin film transistor serves as a switch to turn on/off the pixels, each of which has first and second electrodes facing each other, with the second electrode being used as a common electrode.
When an organic electro luminescence (OEL) layer is formed at a luminescence area of an active matrix OEL device according to a related art, an exposure portion of an insulating film is provided to form the organic electro luminescence layer area in every pixel. However, a new approach to forming an OEL layer for an OEL device has been recently introduced in which an ink-type organic electro luminescence material is directly dispensed in every luminescence area by an inkjet printing method. This inject printing method is simple and can reduce manufacturing cost, as compared with the other known methods. Furthermore, as the resolution of OEL devices becomes higher, which means an interval between pixels becomes smaller, a pixel structure with a barrier is proposed in which the barrier is mainly used for preventing ink-type OEL material dispensed at a luminescence area from being diffused into a non-luminescence area. This barrier also stabilizes the ink-type OEL material dispensed at a luminescence area and is used for patterning a cathode in a subsequent process.
FIG. 1 is a schematic plan view illustrating the panel of an organic electro luminescence device according to a related art, FIG. 2 is a schematic sectional view taken along the line A-A′ in FIG. 1, illustrating a pixel at a center portion of the panel in FIG. 1, and FIG. 3 is a schematic sectional view taken along the line B-B′ in FIG. 1, illustrating a pixel at an edge portion of the panel in FIG. 1.
As shown in FIG. 1, the related-art organic electro luminescence device includes a plurality of pixels 111 in a display area 101. Each of the pixels 111 emits or does not emit light by a switching function of a thin film transistor (not shown). Additionally, reference numeral 122 denotes a barrier provided between the pixels 111. Further, as shown FIGS. 2 and 3, the related-art organic electro luminescence device includes an anode 201 formed of a transparent conductive material on a substrate 200, and a buffer layer 202 formed on the anode 201. Additionally, a barrier 203 is formed on the buffer layer 202 with a predetermined height. An organic electro luminescence layer 205 is formed in each of the pixels. Each of the pixels 111 has a bank structure with the barrier 122 and 203. The barrier 122 and 203 prevents an organic electro luminescence material from being diffused from a pixel area to a non-pixel area. The organic electro luminescence material is coated by an inkjet method at the pixel areas.
When the organic electro luminescence material is coated by an inkjet method, droplets containing the organic electro luminescence material are instantaneously volatilized due to their strong volatility such that the organic electro luminescence material is coated and dried in the pixels. At this time, a center portion of the display area at which many pixels are arranged have a high concentration of the volatile solvent molecules of the droplets, while an edge portion has a low concentration of the volatile solvent molecules of the droplets. Accordingly, the concentration of the solvent molecules varies depending on the location of the display area. Such a concentration difference causes the solvent molecules to diffuse from a center portion having a high concentration to an edge portion having a low concentration. Due to such a diffusion phenomenon, the organic electro luminescence layer in the pixels at the edge portion of the display area has a non-uniform shape, when it dries, as shown in FIG. 3.
Accordingly, as shown in FIG. 2, the organic electro luminescence layer at a center portion of the display area dries uniformly. However, as shown in FIG. 3, the organic electro luminescence layer at an edge portion of the display area dries unevenly due to a concentration difference of the solvent molecules. The unevenness of the organic electro luminescence layer causes luminance irregularity, leading to display failure and product failure.